The present invention is directed to an apparatus and a process for polishing or machining workpieces, particularly wafers such as semi-conductor wafers.
With the rapid growth of the computer industry, competition for computer components has escalated. The price of producing chips can be decreased by increasing the number of chips processed simultaneously. Further, additional capacity can be realized if both sides of the chip are processed (for example, polished) simultaneously. Capacity, and realized cost, can be increased by minimizing the number of damaged or defective chips or wafers. There have been numerous machines disclosed directed at improved wafer processing. For example, a bilateral polishing or lapping process for semiconductor wafers is described in U.S. Pat. No. 3,691,694 and in an article published in the IBM Technical Disclosure Bulletin, Vol. 15, No. 6,of November 1972,pages 1760-1761 (authors: F. E. Goetz and J. R. Hause). In these publications, carrier disks made of a metal, such as steel plate, or consisting entirely of plastic material are disclosed.
Although metal carrier disks provide long service life, in the course of the machining operation, and especially in the case of semiconductor wafers that are often brittle and sensitive to mechanical stresses, the edges of the wafer are damaged and thus, a large portion of the machined wafers cannot be used. It has been realized that this edge damage does not appear in wafers machined using carrier disks made of plastic material. However, as mentioned above, the service life of plastic carrier disks is short. The external periphery of plastic carrier disks cannot withstand the mechanical stresses caused by a drive unit comprising planetary gearing.
The object of the present invention is to provide an apparatus and a process that allows bilateral abrasive machining, such as lapping or polishing, of wafer-like workpieces that causes low mechanical stressing of the edge of the workpiece together with a long service life of the carrier disks.
According to the present invention, an apparatus and a process for bilateral abrasive machining of brittle and stress sensitive material is provided. The apparatus comprises a carrier disk wherein at least the outer periphery is made of a first material and the portion of the carrier disk that comes into contact with the external periphery of the workpiece comprises a plastic material. The plastic material may be formed as an insert that is held within the first material of the carrier disk by at least one layer of adhesive. The adhesive extends parallel to the surface of both the first material and the plastic material, and may cover the entire surface of the carrier disk. That is, the plastic insert is preferably laminated to the first material of the carrier disk. In some embodiments, a layer of adhesive extends parallel to each of opposite first and second surfaces of both the first material and the plastic material. In such an embodiment, the first material and plastic material would be laminated between the two adhesive layers. The strength of the adhesive layer(s) is sufficient to retain the plastic insert securely in the first material.
In one embodiment, the first material may have a tensile strength of at least 100 N/mm2. In another embodiment, the plastic material which contacts the workpiece may have an elastic modulus of about 1.0 to 8.104 N/mm2. However, other materials, with different tensile strengths and elastic moduli, may be used.
In particular, the present invention is directed to an apparatus for use in the machining of a workpiece, such as a silicon wafer or the like. The apparatus comprises a planar carrier disk which comprises a first portion comprising a base plate and a second portion within a first aperture within the first portion. The first aperture is configured and adapted to receive the second portion. The carrier disk or first portion may have a serrated outer periphery. The second portion comprises a second aperture therein, the aperture configured and adapted to receive a workpiece such as a silicon wafer. The second portion comprises a plastic material, which is held within the second portion by at least one layer of adhesive extending across both the first portion and the second portion. Optionally, two layers of adhesive may be used, one on each side of the carrier disk. Preferably, a cross-section of the apparatus at the second portion comprises a first adhesive layer, a plastic layer, and a second adhesive layer.